Image pickup device, image pickup apparatus, control method, and program

ABSTRACT

An image pickup device which makes it possible to expand the dynamic range of photometry. The image pickup device comprises a pixel array, a pixel reader, a row selector, a column selector, a gain circuit, a gain selector. The pixel array comprises a plurality of pixels including photoelectric conversion elements and arranged in the horizontal direction and in the vertical direction. The pixel reader reads out selected pixel signals from the pixel array. The gain circuit is capable of having at least two gains set therein, and amplifies and outputs the pixel signals read out from the pixel array by the pixel reader. The gain selector sets different gains in the gain circuit such that pixel signals amplified by the different gains can be obtained for one-time read-out from the pixel array by the pixel reader.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image pickup device adapted toexpand the dynamic range of photometry, an image pickup apparatusincluding the image pickup device, a method of controlling the imagepickup apparatus, and a program for implementing the control method.

2. Description of the Related Art

Today, to perform photometry for controlling exposure, many image pickupapparatuses employ either a method using a compression sensor for use inphotometry or a method using a linear sensor, such as an image pickupsurface. The method using a linear sensor has a smaller measurabledynamic range than the measurable dynamic range provided by the methodusing a compression sensor, and hence cannot accurately photometer anobject of high contrast.

Particularly in a case where strobe light control is performed prior tostrobe shooting by measuring the amount of reflected light reflectedfrom an object by preliminary light emission and calculating the amountof light to be emitted for the shooting based on the measured reflectedlight amount, the amount of reflected light differs largely depending ona shooting situation. For this reason, the result of exposure at thepreliminary light emission may not fall in the dynamic range of thelinear sensor, causing a blackout condition or saturation. In such acase, it is impossible to perform accurate photometry by one-timeexposure.

To cope with the above-mentioned problem, there has been proposed thefollowing technique (see e.g. Japanese Laid-Open Patent Publication(Kokai) No. 2000-187266), in which it is determined, based on the resultof photometry performed by preliminary light emission, whether or notpreliminary light emission is required to be performed once again, andif it is determined that preliminary light emission is required to beperformed again, photometry is carried out again by preliminary lightemission after changing exposure conditions.

Further, a technique for expanding the dynamic range of the linearsensor has been proposed the following technique (see e.g. JapaneseLaid-Open Patent Publication (Kokai) No. 2005-117192), in which using asolid-state image pickup apparatus, a plurality of kinds of summationsof pixel signals of the same color are performed to generate signalsdifferent in the number of added pixel signals, and photometry iscarried out based on the output signals.

However, in the technique disclosed in Japanese Laid-Open PatentPublication (Kokai) No. 2000-187266, it is required to carry outpreliminary light emission for photometry a plurality of times, whichincreases a release time lag between a time point a release switchoperates upon depression of a shutter button of the image pickupapparatus and a time point shooting starts to be executed.

Further, the technique disclosed in Japanese Laid-Open PatentPublication (Kokai) No. 2005-117192 is not very compatible with a liveview function (i.e. a function of checking a composition and focusingwhile displaying an image formed on an image pickup device in real time)which is realized using a CMOS as the image pickup device. Morespecifically, the pixel summations cause degraded resolution, whichresults in lowered photometric accuracy.

Differently from a CCD image pickup device, the CMOS image pickup deviceis not capable of transferring electric charges in a single operation,and hence pixel signals are sequentially read out. For this reason, in asituation where a mechanical shutter cannot be used as in the case wherelive view is being performed, exposure is continued even during pixelsignal read-out operation. This makes it necessary, when luminance ishigh, to speed up a read-out operation for reading out pixel signalsfrom the image pickup device by thinning-out reading to prevent normallight from causing saturation of pixel signals, thereby reducingaccumulation time.

However, when the pixel summation method proposed in Japanese Laid-OpenPatent Publication (Kokai) No. 2005-117192 is employed to expand thedynamic range using the CMOS as the image pickup device, not onlythinning-out reading of pixel signals but also the pixel summationcauses degraded resolution. This causes the problem of loweredphotometric accuracy. If it is possible to secure a resolution highenough not to affect photometric accuracy, it is desired to furtherincrease a thinning rate to achieve high-speed read-out of pixel signalsso as to expand the photometric dynamic range toward a high luminanceside.

SUMMARY OF THE INVENTION

The present invention provides an image pickup device, an image pickupapparatus including the image pickup device, a method of controlling theimage pickup apparatus, and a program for implementing the controlmethod, which make it possible to expand the dynamic range ofphotometry.

In a first aspect of the present invention, there is provided an imagepickup device comprising a pixel array formed by a plurality of pixelsincluding photoelectric conversion elements and arranged in a horizontaldirection and in a vertical direction, a pixel read-out unit configuredto read out selected pixel signals from the pixel array, an amplifierunit configured to be capable of having at least two gains set therein,and amplify and output the pixel signals read out from the pixel arrayby the pixel read-out unit, and a gain-setting unit configured to setdifferent gains in the amplifier unit such that pixel signals amplifiedby the different gains can be obtained upon one-time read-out from thepixel array by the pixel read-out unit.

With the arrangement of the image pickup device according to the firstaspect of the present invention, the gains are set in the amplificationunit such that image signals amplified by the respective different gainscan be obtained from the image pickup device by each single read-outoperation for reading out pixel signals from the pixel array. This makesit possible to obtain image signals amplified by the respectivedifferent gains, from the image pickup device in each single read-outoperation, whereby it is possible to expand the dynamic range ofphotometry. Further, since photometry is performed using at least one ofa plurality of kinds of pixel signals amplified by the respectivedifferent gains and obtained from the image pickup device throughpreliminary light emission, it is possible to expand the dynamic rangeof photometry, and perform accurate photometry by one-time exposure.

The image pickup device further comprises a row-selecting unitconfigured to select a plurality of pixels from the pixel array in thehorizontal direction, and the gain-setting unit can set gains for rowsselected by the row-selecting unit at intervals of a predeterminednumber of rows.

The image pickup device further comprises a column-selecting unitconfigured to select a plurality of pixels from the pixel array in thevertical direction, and the gain-setting unit can set gains for columnsselected by the column-selecting unit at intervals of a predeterminednumber of columns.

The pixel read-out unit is capable of performing pixel-thinning out forthe pixel array in the horizontal direction or in the vertical directionat predetermined thinning intervals to read out the pixel signals.

In a second aspect of the present invention, there is provided an imagepickup apparatus comprising an image pickup device including a pixelarray formed by a plurality of pixels including photoelectric conversionelements and arranged in a horizontal direction and in a verticaldirection, a pixel read-out unit configured to read out selected pixelsignals from the pixel array, an amplifier unit configured to be capableof having at least two gains set therein, and amplify and output thepixel signals read out from the pixel array by the pixel read-out unit,and a gain-setting unit configured to set different gains in theamplifier unit such that pixel signals amplified by the different gainscan be obtained upon one-time read-out from the pixel array by the pixelread-out unit, a photometric unit configured to measure reflected lightfrom an object caused by preliminary light emission performed beforeshooting, based on the pixel signals read out from the image pickupdevice, a light emission amount-calculating unit configured to calculatea light emission amount required for the shooting, based on a result ofthe photometric measurement by the photometric unit, a light-emittingunit configured to emit light in an amount corresponding to a result ofthe calculation by the light emission amount-calculating unit, and apreliminary light emission photometric unit configured to control theamplifier unit for accumulation of pixel signals in the image pickupdevice during the preliminary light emission, and perform photometryusing at least one of a plurality of kinds of pixel signals amplified bydifferent gains and obtained from the image pickup device.

The image pickup apparatus further comprises a normal light photometricunit configured to control the amplifier unit for accumulation of pixelsignals in the image pickup device under a normal light condition, andperform normal light photometry using at least one of a plurality ofkinds of pixel signals amplified by different gains and obtained fromthe image pickup device, and gain configuration of the amplifier unitfor the accumulation of pixel signals in the image pickup device underthe normal light condition is identical to gain configuration of theamplifier unit for the accumulation of pixel signals in the image pickupdevice during the preliminary light emission.

The image pickup apparatus can have a live view function forsequentially display images based on the pixel signals read out from theimage pickup device.

In a third aspect of the present invention, there is provided a methodof controlling an image pickup apparatus having an image pickup deviceincluding a pixel array formed by a plurality of pixels includingphotoelectric conversion elements and arranged in a horizontal directionand in a vertical direction, a pixel read-out unit configured to readout selected pixel signals from the pixel array, an amplifier unitconfigured to be capable of having at least two gains set therein, andamplify and output the pixel signals read out from the pixel array bythe pixel read-out unit, and a gain-setting unit configured to setdifferent gains in the amplifier unit such that pixel signals amplifiedby the different gains can be obtained upon one-time read-out from thepixel array by the pixel read-out unit, the method comprising aphotometric measurement step of measuring reflected light from an objectcaused by preliminary light emission performed before shooting, based onthe pixel signals read out from the image pickup device, a lightemission amount-calculating step of calculating a light emission amountrequired for the shooting, based on a result of the photometricmeasurement in the photometric measurement step, a light-emitting stepof emitting light in an amount corresponding to a result of thecalculation in the light emission amount-calculating step, and apreliminary light emission photometric measurement step of controllingthe amplifier unit for accumulation of pixel signals in the image pickupdevice during the preliminary light emission, and perform photometryusing at least one of a plurality of kinds of pixel signals amplified bydifferent gains and obtained from the image pickup device.

In a fourth aspect of the present invention, there is provided a programfor causing a computer to execute a method of controlling an imagepickup apparatus having an image pickup device including a pixel arrayformed by a plurality of pixels including photoelectric conversionelements and arranged in a horizontal direction and in a verticaldirection, a pixel read-out unit configured to read out selected pixelsignals from the pixel array, an amplifier unit configured to be capableof having at least two gains set therein, and amplify and output thepixel signals read out from the pixel array by the pixel read-out unit,and a gain-setting unit configured to set different gains in theamplifier unit such that pixel signals amplified by the different gainscan be obtained upon one-time read-out from the pixel array by the pixelread-out unit, the program comprising a photometric module for measuringreflected light from an object caused by preliminary light emissionperformed before shooting, based on the pixel signals read out from theimage pickup device, a light emission amount-calculating module forcalculating a light emission amount required for the shooting, based ona result of the photometric measurement by the photometric measurementmodule, a light-emitting module for emitting light in an amountcorresponding to a result of the calculation by the light emissionamount-calculating module, and a preliminary light emission photometricmodule for controlling the amplifier unit for accumulation of pixelsignals in the image pickup device during the preliminary lightemission, and perform photometry using at least one of a plurality ofkinds of pixel signals amplified by different gains and obtained fromthe image pickup device.

The features and advantages of the invention will become more apparentfrom the following detailed description taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a solid-state image pickup device accordingto a first embodiment of the present invention.

FIG. 2 is a schematic view useful in explaining read gains forrespective pixel rows.

FIG. 3 is a schematic view useful in explaining read gains forrespective pixel rows.

FIG. 4 is a schematic view useful in explaining read gains forrespective pixel columns.

FIG. 5 is a block diagram of a digital camera system as an image pickupapparatus according to a second embodiment of the present invention.

FIG. 6 is a flowchart of a shooting process carried out by the imagepickup apparatus.

FIG. 7 is a flowchart of a strobe light control process.

FIG. 8 is a schematic diagram showing a read-out time and anaccumulation time in an image pickup device drive method (rollingshutter read-out method).

FIG. 9 is a schematic diagram showing a read-out time and anaccumulation time in another image pickup device drive method (slitrolling shutter read-out method).

FIG. 10 is a schematic view useful in explaining read gains forrespective pixel rows.

FIG. 11 is a schematic diagram showing a distance range where photometryis possible.

FIG. 12 is a diagram showing the relationship between external lightluminance and strobe reflected light.

FIG. 13 is a diagram useful in explaining the relationship betweenthinning-out of pixels and accumulation time in a slit rolling shutterdrive operation.

FIG. 14 is a diagram useful in explaining the relationship between thethinning-out of pixels and the accumulation time in the slit rollingshutter drive operation, which illustrates a case where pixel signalsare read out from the image pickup device by a method of “nothinning-out in the horizontal direction and one-third thinning-out inthe vertical direction”.

FIG. 15 is a diagram useful in explaining the relationship between thethinning-out of pixels and the accumulation time in the slit rollingshutter drive operation, which illustrates a case where pixel signalsare read out from the image pickup device by a method of “one-halfthinning-out in the horizontal direction and no thinning-out in thevertical direction”.

FIG. 16 is a diagram useful in explaining the relationship between thethinning-out of pixels and the accumulation time in the slit rollingshutter drive operation, which illustrates a case where pixel signalsare read out from the image pickup device by a method of “one-halfthinning-out in the horizontal direction and one-third thinning-out inthe vertical direction”.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail with reference tothe drawings showing a preferred embodiment thereof.

FIG. 1 is a block diagram of a solid-state image pickup device accordingto a first embodiment of the present invention.

Referring to FIG. 1, the solid-state image pickup device (hereinaftersimply referred to as “the image pickup device”) according to thepresent embodiment is capable of obtaining output signals for differentlevels of brightness in each single read-out operation. The image pickupdevice is comprised of a pixel array 1, a pixel reader 2, a row selector3, a column selector 4, a gain circuit 5, and a gain selector 6.

The pixel array 1 is comprised of a plurality of pixels, includingphotoelectric conversion elements, which are arranged in a horizontaldirection and in a vertical direction. The row selector 3 selects aplurality of pixels from the pixel array 1 in the horizontal direction.The column selector 4 selects a plurality of pixels from the pixel array1 in the vertical direction. The pixel reader 2 is capable of readingout pixels from the pixel array 1 at a high speed by performing pixelthinning in the horizontal direction or in the vertical direction atpredetermined intervals. The pixel reader 2 sequentially reads out pixelsignals selected by each of the row selector 3 and the column selector4.

The gain selector 6 sets a plurality of kinds of different gains foreach of the rows and columns of the pixel array 1 of the gain circuit 5for one-time read-out of pixel signals. The gain circuit 5 is configuredsuch that a plurality of kinds of different gains can be set therein,and amplifies and outputs pixel signals based on associated gainsselected by the gain selector 6. The gain selector 6 sets gains in thegain circuit 5 for respective rows selected from the pixel array 1 bythe row selector 3 at intervals of a predetermined number of rows.Further, the gain selector 6 sets gains in the gain circuit 5 forrespective columns selected from the pixel array 1 by the columnselector 4 at intervals of a predetermined number of columns.

FIG. 2 is a schematic view useful in explaining read gains forrespective pixel rows.

FIG. 2 illustrates an example of selection of gains by the gain selector6 for read-out of respective pixel signals from the pixel array shown inFIG. 1. A gain ISO100 and a gain ISO400 are alternately selected everytwo rows of the pixel array, and signals amplified by two differentkinds of gains, respectively, are read out in each single pixel signalread-out operation. In the present embodiment, the pixel array isillustrated by 12 rows×8 columns for simplicity of explanation. Itshould be noted that although in the present embodiment, the two gainsISO100 and ISO400 are selected, the values and kinds of gains to beselected are not limited to those in the above-described example.

FIG. 3 is a schematic view useful in explaining read gains forrespective pixel rows.

FIG. 3 illustrates an example of a case where pixels are read out bythinning-out reading from the pixel array shown in FIG. 2. In thepresent embodiment, a read-out operation is performed while thinning outone for every three rows, and the gains ISO100 and ISO400 are selectedalternately for the rows read out. By thus carrying out thinning-outreading of pixels, it is possible to increase the speed at which eachread-out operation is performed. Although in the present embodiment, aread-out operation is performed while thinning out one for every threerows (i.e. at a one-third thinning-out interval), this is notlimitative.

FIG. 4 is a schematic view useful in explaining read gains forrespective pixel columns.

FIG. 4 shows an example of a case where a gain for a pixel signal to beread out is selected by the gain selector 6 for each column of the pixelarray, and a read-out operation is performed while thinning out one forevery three columns. In the present embodiment, the gain ISO100 and again ISO800 are alternately selected for columns to be read out.Although in the present embodiment, one column is thinned out everythree columns of the pixel array, and the two different kinds of gainsare selected, the thinning-out interval, the gain values, and the numberof kinds of gains are not limited to those in the above-describedexample.

As described above, according to the present embodiment, it is possibleto obtain image signal outputs amplified by a plurality of differentkinds of gains, in a single read-out operation. This makes it possibleto expand the dynamic range of image signal outputs obtained by one-timeexposure. The same advantageous effects as described above can beobtained in a case where high-speed read-out of pixels from the pixelarray is performed by executing thinning-out reading of pixels therefromin combination.

FIG. 5 is a block diagram of a digital camera system as an image pickupapparatus according to a second embodiment of the present invention.

As shown in FIG. 5, the digital camera system is a digital single-lensreflex camera (hereinafter simply referred to as “the digital camera”)100, a photographic lens unit 200, and a stroboscopic device 300 withthe camera 100 is equipped. The digital camera 100 includes an opticalmechanism, various kinds of circuits, various kinds of operationbuttons, referred to hereinafter, and a system controller (CPU) 120. Thephotographic lens unit 200 is detachably attached to the digital camera100 via a mount mechanism (not shown). The photographic lens unit 200includes a photographic lens 201, and an aperture 202. The mountmechanism has an electric contact group 210. The system controller 120and the electric contact group 210 constitute a lens-detecting section.

The electric contact group 210 has a function of transferring controlsignals, state signals, data signals, and so forth, between the digitalcamera 100 and the photographic lens unit 200. The electric contactgroup 210 also has a function of supplying various kinds of voltages andelectric currents and a function of transmitting signals to the systemcontroller 120 when the photographic lens unit 200 is connected to thedigital camera 100. Communication between the digital camera 100 and thephotographic lens unit 200 makes it possible to drive the photographiclens 201 and the aperture 202 within the photographic lens unit 200. Theelectric contact group 210 may be configured to have not only thefunction for electrical communication, but also a function for opticalcommunication, a function for voice communication, and like functions.

Although in the present embodiment, only a single photographic lens isshown in FIG. 5 for convenience of description, it is to be understoodthat the photographic lens unit 200 has a larger number of photographiclenses in actuality.

In accordance with a shooting operation by the image pickup apparatus,photographic light flux from an object (not shown) is guided through thephotographic lens 201 and the aperture 202 to a quick return mirror 102which can be driven in a direction indicated by an arrow in FIG. 5. Thequick return mirror 102 has a central part thereof formed as a halfmirror. When the quick return mirror 102 is in its down position, partof photographic light flux passes through the central part of the quickreturn mirror 102. The photographic light flux having passed through thequick return mirror 102 is reflected downward by a sub mirror 103attached to the quick return mirror 102.

An AF sensor unit 104, which executes a known phase difference-detectingmethod, is comprised of a field lens disposed in the vicinity of animage forming surface, a reflective mirror, a secondary image forminglens, an aperture, and a line sensor comprised of a plurality of CCDs,none of which are shown. A focus-detecting circuit 105 controls the AFsensor unit 104 based on a control signal from the system controller 120to thereby perform focus detection by the phase difference-detectingmethod. The AF sensor unit 104 and the focus-detecting circuit 105constitute a focus-detecting section.

On the other hand, photographic light flux reflected by the quick returnmirror 102 reaches a photographer's eye through a pentagonal prism 101and an eyepiece 106. When the quick return mirror 102 is in its upposition, photographic light flux having passed through the photographiclens 201 reaches an image sensor 112 as an image pickup device through afocal plane shutter 108 as a mechanical shutter and a filter 109. Theimage sensor 112 is specifically implemented by a CMOS image sensor.

It should be noted that the image sensor 112 corresponds to thesolid-state image pickup device described in the first embodiment. Theimage sensor 112 is a solid-state image pickup device capable of settinggains at predetermined intervals for respective rows selected by the rowselector and obtaining output signals for different levels of brightnessin a single read-out operation. Further, it is assumed that the imagesensor 112 is capable of reading out pixel signals at a high speed whilethinning out pixels in the horizontal direction and the verticaldirection.

The filter 109 has both a function of filtering out infrared radiationand guiding only visible radiation to the image sensor 112 and afunction as an optical low-pass filter. The focal plane shutter 108 hasfront and rear curtains and controls transmission and blockage of lightflux from the photographic lens 201. It should be noted that when thequick return mirror 102 is in its up position, the sub mirror 103 isheld in a folded state.

The system controller 120 is formed by the CPU that controls the overalloperation of the digital camera system. The system controller 120controls the operation of each section, described hereinafter, asrequired, and executes processes described hereinafter with reference toFIGS. 6 and 7, based on programs. Further, the system controller 120 hasa photometric function and a light emission amount-calculating function.A lens control circuit 204 and an aperture control circuit 206 areconnected to the system controller 120. The lens control circuit 204controls a lens drive mechanism 203 for moving the photographic lens 201in the optical axis direction for focusing. The aperture control circuit206 controls an aperture drive mechanism 205 for driving the aperture202.

Further, a shutter charge/mirror drive mechanism 110, a shutter controlcircuit 111, and a photometry circuit 107 are connected to the systemcontroller 120. The shutter charge/mirror drive mechanism 110 controlsdriving of the up/down operation of the quick return mirror 102 and theshutter charge of the focal plane shutter 108. The shutter controlcircuit 111 controls the travel of each of the front and rear curtainsof the focal plane shutter 108. The photometry circuit 107 is connectedto a photometric sensor (not shown) disposed in the vicinity of theeyepiece 106 to perform automatic exposure.

Further, an EEPROM 122 is connected to the system controller 120. TheEEPROM 122 stores parameters required to be adjusted for controlling thedigital camera system, camera ID information for identifying the digitalcamera, AF correction data adjusted by a reference lens, automaticexposure correction values, and so forth.

The lens control circuit 204 includes a lens storage section (not shown)storing lens-specific information (focal distances of the respectivelenses, wide open aperture value, lens IDs assigned to the respectivelenses, etc., for example) and information received from the systemcontroller 120. The photometric sensor connected to the photometrycircuit 107 is configured to measure the luminance of an object, and anoutput therefrom is delivered to the system controller 120 via thephotometry circuit 107.

The system controller 120 controls the lens drive mechanism 203 by thelens control circuit 204 to thereby form the image of an object on theimage sensor 112. Further, the system controller 120 controls theaperture drive mechanism 205 by the aperture control circuit 206 basedon a set Av (aperture amount) value, and outputs a control signal to theshutter control circuit 111 based on a set Tv (parameter correspondingto the shutter speed) value.

The front and rear curtains of the focal plane shutter 108 have a drivesource formed by a spring, and hence need spring charge for an operationfollowing shutter travel. The shutter charge/mirror drive mechanism 110is configured to control the spring charge. Further, the shuttercharge/mirror drive mechanism 110 turns up/down the quick return mirror102, as described hereinabove.

Further, an image data controller 115 is connected to the systemcontroller 120. The image data controller 115 is implemented by a DSP(digital signal processor), and performs control of the image sensor 112and correction/processing of image data received from the image sensor112 in response to instructions from the system controller 120. Theimage data correction/processing includes auto white balance correction.The auto white balance is a function of correcting a maximum-luminanceportion of a picked-up image to a predetermined color (white). Theamount of the correction can be changed following a command from thesystem controller 120.

The system controller 120 and the image data controller 115 constitute asecond photometry section. The second photometry section performs thefollowing processing: The image data controller 115 divides an imagesignal into regions, and delivers values obtained by performing Bayerpixel-by-Bayer pixel integration in the respective regions to the systemcontroller 120. The system controller 120 performs photometry byevaluating the integrated signals.

Connected to the image data controller 115 are a timing pulse-generatingcircuit 114, an A/D converter 113, a D/A converter 116, an imagecompression circuit 119, a DRAM 121, and a contrast-detecting circuit140. The timing pulse-generating circuit 114 outputs a pulse signalrequired for driving the image sensor 112.

Together with the image sensor 112, the A/D converter 113 receive thetiming pulse generated by the timing pulse-generating circuit 114, andconverts an analog signal associated with an object image output fromthe image sensor 112 into a digital signal. The DRAM 121 temporarilystores obtained image data (digital signals). More specifically, theDRAM 121 is used to temporarily store image data to be subjected toprocessing and data conversion into a predetermined format.

A storage medium 401 is connected to the image compression circuit 119.The image compression circuit 119 is configured to perform compressionand conversion (e.g. JPEG compression) of image data stored in the DRAM121. Image data subjected to the conversion is stored in the storagemedium 401. The storage medium is implemented e.g. by a hard disk, aflash memory or a floppy (registered trademark) disk. It should be notedthat the image data controller 115, the image compression circuit 119,and the storage medium 401 constitute a recording section.

An image display circuit 118 is connected to the D/A converter 116 viaan encoder circuit 117. The image display circuit 118 displays imagedata picked up by the image sensor 112. The image display circuit 118 isgenerally implemented by a color liquid crystal display device.

The image data controller 115 converts image data stored in the DRAM 121into an analog signal by the D/A converter 116, and outputs the analogsignal to the encoder circuit 117. The encoder circuit 117 converts theoutput from the D/A converter 116 into a video signal (e.g. an NTSCsignal) required for driving the image display circuit 118. It should benoted that the D/A converter 116, the image display circuit 118, and theencoder circuit 117 constitute an image display section.

Based on instructions from the system controller 120, thecontrast-detecting circuit 140 executes the following processing: Thecontrast-detecting circuit 140 evaluates a contrast in a predetermineddirection of an image signal obtained by passing image data corrected bythe image data controller 115 through a filter having a predeterminedfrequency characteristic and performing predetermined gamma processingon the image data. The result of the contrast evaluation is supplied tothe system controller 120.

Further, connected to the system controller 120 are a communication I/Fcircuit 126, an operation display circuit 123, the various kinds ofselection buttons, and various kinds of switches. The communication I/Fcircuit 126 provides interface for communication with an informationprocessing apparatus 400. The operation display circuit 123 causes anexternal liquid crystal display 124 and an internal liquid crystaldisplay 125 to display information on an operation mode of the digitalcamera, exposure information (a shutter second time, an aperture value,etc.), and so forth. It should be noted that the operation displaycircuit 123 and the system controller 120 constitute a display controlsection.

A shooting mode selection button 130 is operated by the photographer toset a mode for causing the digital camera to perform a desiredoperation. A ranging point selection button 133 is operated to select afocal point detecting position for use from a plurality of focal pointdetecting positions provided for the AF sensor unit 104. An AF modeselection button 134 is operated to select an AF mode. A photometry modeselection button 135 is operated to select a photometry mode. A releaseswitch 1 136 is operated to start a shooting preparation operation, suchas photometry and ranging. A release switch 2 137 is operated to startan image pickup operation.

A finder mode selection button 138 is operated to switch between anoptical finder mode and a live view mode. The optical finder mode makesit possible to check a photographic light flux passing through theeyepiece 106. The live view mode makes it possible to cause the imagedisplay circuit 118 to sequentially display object image signals(images) received by the image sensor 112.

Further, the stroboscopic device 300 is attached to the digital camera100 via a mount mechanism (not shown). The mount mechanism is providedwith an electric contact group 310. The electric contact group 310 has afunction of transferring control signals, state signals, data signals,and so forth, between the digital camera 100 and the stroboscopic device300. The electric contact group 310 also has a function of transmittinga signal to the system controller 120 when the stroboscopic device 300is connected to the digital camera 100. Communication between thedigital camera 100 and the stroboscopic device 300 makes it possible tocontrol light emission of a stroboscope. The electric contact group 310may be configured to have not only the function for electricalcommunication, but also a function for optical communication, a functionfor voice communication, and like functions.

Next, the operation of the digital camera system constructed as abovewill be described in detail with reference to FIGS. 6 to 16.

FIG. 6 is a flowchart of a shooting process carried out by the imagepickup apparatus, and

FIG. 7 is a flowchart showing a strobe light control process in detail.

As shown in FIG. 6, the system controller 120 of the digital cameradetermines whether or not the photographer has operated the finder modeselection button 138 to give an instruction for starting (turn-on) ofthe live view mode (step S101. When the photographer operates the findermode selection button 138 to notify the system controller 120 of thestarting of the live view mode, the system controller 120 performs thefollowing control: The system controller 120 brings the quick returnmirror 102 into the UP state and opens the focal plane shutter 108 tothereby perform control such that photographic light flux passingthrough the photographic lens 200 holds the image sensor 112 in theexposed state.

Next, the system controller 120 performs a live view operation (stepS102). More specifically, the system controller 120 switches the methodof driving the image sensor 112 to a slit rolling shutter read-outmethod to convert pixel signals sequentially read out from the imagesensor 112 into digital signals by the A/D converter 113. Then, thesystem controller 120 performs image processing on the digital signalsby the image data controller 115, converts the processed digital signalsinto analog signals by the D/A converter 116, encodes the analogsignals, and transmits the encoded analog signals to the DRAM 121.Further, the system controller 120 sequentially displays images on theexternal liquid crystal display 124.

Now, the method of driving the image sensor 112 during the live viewoperation will be briefly described with reference to FIGS. 8 and 9. Inthe case of realizing the live view function, it is required tosequentially read out pixel signals. The CMOS image pickup device is notcapable of transferring pixel signals or reading out pixel signals in asingle operation as a CCD image pickup device is, and hence a rollingshutter read-out method is generally employed.

In the rolling shutter read-out method shown in FIG. 8, in synchronismwith the timing of respective VD (Vertical Drive) signals, pixels arereset, and then electric charges (pixel signals) are accumulated inrespective photo diodes (hereinafter referred to as “the PDs”) of theimage sensor 112 and read out, sequentially from the uppermost line ofan image area to the lowermost one, on a horizontal line-by-horizontalline basis. In short, pixel reset is instructed in the timing of each VDsignal. For this reason, in one frame of image, there occurs a time lagin the operation of accumulation and read-out from line to line, and atime lag between the uppermost line and the lowermost line depends onthe read-out speed per one line and the number of vertical lines.Further, an accumulation time is limited by a time period required forreading out one frame of image.

In the slit rolling shutter read-out method shown in FIG. 9, it ispossible to perform pixel reset in desired timing along a pixel resetline (slit), thereby resetting electric charges accumulated in therespective PDs to change the accumulation time. In short, pixel reset isinstructed in timing different from timing of the VD signal. Further, inthe slit rolling shutter read-out method, it is possible to adjust theaccumulation time in combination with the automatic exposure controlfunction to thereby obtain pixel signals adjusted to a desired exposureamount from the image pickup device. It should be noted that the resetline is designated by a symbol Rec in FIG. 9.

Further, when the read-out time is limited by frame rate as in the caseof the live view operation, it is required to perform reading of onlysome areas of a full screen area or to perform thinning-out of pixels inthe horizontal and vertical directions to thereby read out pixel signalsat a high speed.

In the live view operation in the step S102, photometry is performed bythe second photometry section (the system controller 120 and the imagedata controller 115) based on the read-out pixel signals. Further, theaperture and the accumulation time are controlled by the automaticexposure control function, and gains are set in the gain circuit, tothereby adjust exposure. At the same time, strobe automatic lightemission determination is performed to automatically determine whetheror not to cause the stroboscopic device 300 to emit light.

When the photographer presses the release switch 1 136, the processproceeds to a step S103, wherein the system controller 120 communicateswith the lens control circuit 204 based on the result of output from thecontrast-detecting circuit 140 and adjusts a focus state. When the focusstate is completely adjusted, the process proceeds to a step S104.

Similarly to the live view operation, the system controller 120 performsphotometry based on the image signals read out from the image sensor 112to calculate a Bv value for shooting (step S104). The Bv value is anindicator indicative of a luminance level, and is obtained by anequation of Bv=Tv+Av−Sv. In the equation, Tv represents a parametercorresponding to the shutter speed (corresponding to accumulation time),Av a parameter corresponding to the aperture amount, and Sv a parametercorresponding to the gain level, such as the ISO sensitivity and thelike. When photometry is completed, the process proceeds to a step S105.

The system controller 120 holds the Bv value for shooting during a timeperiod over which the release switch 1 136 is kept on, and performs alive view operation (step S105). Further, the system controller 120continuously performs photometry and strobe automatic light emissiondetermination. When the photographer turns off the release switch 1 136,the system controller 120 abandons the held Bv value for shooting,followed by the process returning to the step S102.

When the photographer presses the release switch 2 137, the systemcontroller 120 determines, based on a strobe light emission condition(forcible light emission, automatic light emission, or inhibition oflight emission) configurable by the photographer and the result of theautomatic light emission determination, whether or not strobe shootingis to be performed (step S106). If it is determined that strobe shootingis required, the system controller 120 performs strobe light control(step S107). The strobe light control will be described hereinafter withreference to FIG. 7. On the other hand, if it is determined that strobeshooting is not required, the system controller 120 holds the Bv valuefor shooting, which was calculated in the step S104, and the processproceeds to a step S108.

Referring to FIG. 7, the system controller 120 configures exposurecontrol for photometry (step S201). First, the system controller 120sets a predetermined aperture value and a predetermined accumulationtime based on the latest photometry result obtained in the step S105.Further, the system controller 120 sets a first gain circuit setting toa value corresponding to ISO100, and a second gain circuit setting to adifferent value (e.g. ISO3200) from the first gain circuit setting.

Thus, it is possible to obtain a first signal output and a second signaloutput from the image sensor 112, as shown in FIG. 10. The first signaloutput and the second signal output are obtained by performing exposure,accumulation, and the read-out in the same timing, so that they areoutput with the respective exposure levels shifted by a differencebetween the first and second gain circuit settings. When configurationof exposure control in light control is completed, the process proceedsto a step S202.

The system controller 120 performs normal light photometry for measuringnormal light under the exposure conditions set in the step S201 (stepS202). Further, the system controller 120 stores a first normal lightsignal output E1 a obtained from the first signal output and a secondnormal light signal output E2 a obtained from the second signal outputin the EEPROM 122. When the normal light photometry is completed, theprocess proceeds to a step S203.

In the normal light photometry, the gain circuit is adjusted toaccumulate pixel signals in the image sensor 112 under a normal lightcondition, and the normal light photometry is performed using at leastone of a plurality of kinds of pixel signals which are different in gainand obtained from the image sensor 112.

The system controller 120 performs preliminary light emission beforeshooting in a predetermined light emission amount, under the exposureconditions set in the step S201, to thereby carry out preliminary lightemission photometry to measure reflected light (mixed light) reflectedfrom an object in the preliminary light emission (step S203). As aresult, the system controller 120 can obtain a first preliminary lightemission signal output E1 b from the first signal output and a secondpreliminary light emission signal output E2 b from the second signaloutput. When the preliminary light emission photometry is completed, theprocess proceeds to a step S204.

In the preliminary light emission photometry, the gain circuit isadjusted to accumulate pixel signals in the image sensor 112 under apreliminary light emission condition, and photometry is performed usingat least one of a plurality of kinds of pixel signals which obtainedfrom the image sensor 112 by different gains.

The gain configuration for the gain circuit in the accumulation of pixelsignals in the image sensor 112 under the normal light condition isidentical to that under the preliminary light emission condition.

The system controller 120 determines the amount of reflected light fromthe object to be caused light emission by the stroboscopic device 300,using the signal outputs as results of the respective steps S202 andS203, and calculates the amount of light emission required for the mainshooting (step S204). The amount of reflected light to be reflected fromthe object can be calculated in the following manner: A first reflectedlight amount R1 and a second reflected light amount R2 can be calculatedby determining respective differences between the first and secondpreliminary light emission signal outputs (E1 b and E2 b) obtained inthe step S203 and the first and second normal light signal outputs (E1 aand E2 a) obtained in the step S202.

R1=E1b−E1a

R2=E2b−E2a

Further, the amount of light emission is calculated based on theobtained first and second reflected light amounts R1 and R2 and theexposure parameters, such as the shutter speed, the aperture value, theISO sensitivity for shooting, which were obtained from the photometryexecuted in the step S104. It should be noted that this does not applyto manual exposure.

Next, a description will be given of a dynamic range within which lightcan be adjusted by the strobe light control. Assuming that the dynamicrange of the image pickup device used for photometry has +3 stages andthat the influence of normal light is sufficiently negligible, when theexposure conditions are properly set in the step S201, a distance withinwhich light is adjustable can be calculated as follows:

As shown in FIG. 11, it is possible to calculate a distance between theimage pickup device and a reflector plate with a reflectivity of 18%,which is approximately 0.71 m to 5.66 m away, based on the firstreflected light amount R1. Further, it is possible to calculate adistance between the image pickup device and a reflector plate with areflectivity of 18%, which is approximately 4.00 m to 32 m away, basedon the second reflected light amount R2. In other words, in terms ofstages which can be set within a distance range, shown in FIG. 11, thefirst reflected light amount R1 and the second reflected light amount R2are shifted from each other by five stages. This makes it possible toextend the distance range allowing photometry by five stages byobtaining the first and second signal outputs through accumulation andread-out of pixel signals by one-time preliminary light emission.

FIG. 12 shows the relationship between external light luminance andstrobe reflected light (exposure conditions). When the luminance ofnormal light is low, the influence of external light is smaller, andhence the strobe reflected light becomes dominant. Therefore, bycontrolling the accumulation time with the aperture open, it is possibleto obtain a desired amount of strobe reflected light. However, when theluminance of normal light is high, the accumulation time reaches a highspeed-side control limit, which disables desired control. Therefore, itis impossible to eliminate external light.

When external light cannot be eliminated, it is required to drive theaperture to control the exposure conditions. However, when the apertureis driven, even reflected light as a strobe light component is reduced.For this reason, in order to obtain a desired amount of reflected light,there is no alternative but to increase the amount of light emitted forpreliminary light emission. Further, an increase in the amount of lightemitted for preliminary light emission causes an increase in a chargetime for strobe light emission during a main shooting. In short, inorder to eliminate external light, it is required to minimize theaccumulation time and obtain strobe reflected light efficiently.

Next, a minimum accumulation time during strobe light emission in a casewhere the image sensor 112 is driven for a live view operation by theslit rolling shutter drive method will be described with reference toFIGS. 13 to 16.

FIG. 13 is a diagram showing the relationship between thinning-out andthe accumulation time in the slit rolling shutter drive operation. InFIG. 13, there is shown a minimum accumulation time during strobe lightemission in a case where pixel signals are read out from the imagepickup device at intervals of 30 fps (frames per second) withoutperforming thinning-out of pixels either in the horizontal direction orin the vertical direction. When a photometric area covers an entireimage area, preliminary light emission by the stroboscope is required tobe performed such that the entire image area is irradiated with auniform amount of strobe light. For this reason, it is required toperform flat emission over an entire image area exposure time (imagearea read-out time+accumulation time), or to perform light emissionduring a full open section over which the entire image area is exposed.

In the former case (where flat emission is performed over the entireimage area exposure time), a huge amount of energy is needed forpreliminary light emission, and hence the method is not practical.Therefore, the latter method is inevitably employed. In this case,however, the full open section over which the entire image area isexposed is required to be secured as a time period corresponding to atleast a preliminary light emission time plus a control error. As aresult, the rest line to be shifted by the slit rolling function has itsshift range restricted, and hence the accumulation time easily reachesits high speed-side limit. This causes saturation by normal light undera high-luminance condition, which disables light control.

The above problem can be alleviated by increasing read-out speed forreading out pixel signals from the image pickup device. In FIG. 14,there is shown a minimum accumulation time during strobe light emissionin a case where pixel signals are read out from the image pickup deviceby a method of “no thinning-out in the horizontal direction andone-third thinning-out in the vertical direction”. Further, in FIG. 15,there is shown a minimum accumulation time during strobe light emissionin a case where pixel signals are read out from the image pickup deviceby a method of “one-half thinning-out in the horizontal direction and nothinning-out in the vertical direction” condition. Furthermore, in FIG.16, there is shown a minimum accumulation time during strobe lightemission in a case where pixel signals are read out from the imagepickup device by a method of “one-half thinning-out in the horizontaldirection and one-third thinning-out in the vertical direction”condition.

It is understood from FIGS. 14 to 16 that it is possible to shift thelimit of the minimum accumulation time toward the high speed side byincreasing the read-out speed by performing thinning-out read-out ofpixels in the horizontal and vertical directions at predeterminedread-out intervals.

Exposure conditions and a strobe light emission amount for the mainshooting are determined by the strobe light control process executed inthe steps S201 to S204 in FIG. 7, and the shooting process proceeds to astep S108 of the main shooting sequence shown in FIG. 6.

Referring to FIG. 6, if it is not required to perform strobe shooting,the system controller 120 sets exposure conditions for the digitalcamera based on the Bv value for shooting, which was obtained in thestep S104, a shooting mode designated by the user, and the parametersfor shooting. On the other hand, if it is required to perform strobeshooting, the system controller 120 sets the exposure conditions for thedigital camera and the strobe light emission amount based on the resultof the strobe light control process executed in the step S107 (stepS108). When the setting is completed, the process proceeds to a stepS109. It should be noted that here, the first gain circuit setting andthe first gain circuit setting are set to the same value.

The system controller 120 temporarily closes the open focal planeshutter 108 and performs spring charge to drive the front and rearcurtains with the set Tv value. Further, the system controller 120performs a normal image pickup operation (still image pickup operation)for sequentially reading out pixels from the image sensor 112 withoutthinning out pixels (step S109).

Thereafter, the system controller 120 performs image correction on imagesignals read out from the image sensor 112, by the image data controller115, and performs image conversion, such as JPEG compression, by theimage compression circuit 119, followed by recording the image in thestorage medium 401. When the read-out operation for reading out pixelsfrom the image sensor 112 is completed, the system controller 120 holdsthe mirror in the UP state and the shutter curtains in the open state,and returns to the step S102 to resume the live view operation.

Although in the present embodiment, the two kinds of gains are set byway of example, the number of kinds of gains is not limited to this.Further, the rate of thinning-out of pixels is not limitative, either.

As described above, according to the present embodiment, it is possibleto expand the dynamic range within which light can be adjusted by thestrobe light control based on reflected light reflected from an objectthrough one-time preliminary light emission. Further, by using thethinning read-out method in combination, improvement of thehigh-luminance limit in light control under a high-luminance conditioncan be achieved. Furthermore, in a case where normal light photometry isperformed, output signals amplified by a plurality of kinds of gains canbe obtained, and therefore it is possible to expand the dynamic range ofphotometry.

It is to be understood that the present invention may also beaccomplished by supplying a system or an apparatus with a storage mediumin which a program code of software, which realizes the functions ofeither of the above described embodiments is stored, and causing acomputer (or CPU or MPU) of the system or apparatus to read out andexecute the program code stored in the storage medium.

In this case, the program code itself read from the storage mediumrealizes the functions of either of the above described embodiments, andtherefore the program code and the storage medium in which the programcode is stored constitute the present invention.

Examples of the storage medium for supplying the program code include afloppy (registered trademark) disk, a hard disk, a magnetic-opticaldisk, an optical disk, such as a CD-ROM, a CD-ER, a CD-RW, a DVD-ROM, aDVD-RAM, a DVD-RW, or a DVD+RW, a magnetic tape, a nonvolatile memorycard, and a ROM. Alternatively, the program may be downloaded via anetwork.

Further, it is to be understood that the functions of either of theabove described embodiments may be accomplished not only by executingthe program code read out by a computer, but also by causing an OS(operating system) or the like which operates on the computer to performa part or all of the actual operations based on instructions of theprogram code.

Further, it is to be understood that the functions of either of theabove described embodiments may be accomplished by writing a programcode read out from the storage medium into a memory provided on anexpansion board inserted into a computer or a memory provided in anexpansion unit connected to the computer and then causing a CPU or thelike provided in the expansion board or the expansion unit to perform apart or all of the actual operations based on instructions of theprogram code.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all modifications, equivalent structures and functions.

This application claims priority from Japanese Patent Application No.2007-021130 filed Jan. 31, 2007, which is hereby incorporated byreference herein in its entirety.

1. An image pickup device comprising: a pixel array formed by aplurality of pixels including photoelectric conversion elements andarranged in a horizontal direction and in a vertical direction; a pixelread-out unit configured to read out selected pixel signals from saidpixel array; an amplifier unit configured to be capable of having atleast two gains set therein, and amplify and output the pixel signalsread out from said pixel array by said pixel read-out unit; and again-setting unit configured to set different gains in said amplifierunit such that pixel signals amplified by the different gains can beobtained upon one-time read-out from said pixel array by said pixelread-out unit.
 2. An image pickup device as claimed in claim 1, furthercomprising a row-selecting unit configured to select a plurality ofpixels from said pixel array in the horizontal direction, and whereinsaid gain-setting unit sets gains for rows selected by saidrow-selecting unit at intervals of a predetermined number of rows.
 3. Animage pickup device as claimed in claim 1, further comprising acolumn-selecting unit configured to select a plurality of pixels fromsaid pixel array in the vertical direction, and wherein saidgain-setting unit sets gains for columns selected by saidcolumn-selecting unit at intervals of a predetermined number of columns.4. An image pickup device as claimed in claim 1, wherein said pixelread-out unit is capable of performing pixel-thinning out for said pixelarray in the horizontal direction or in the vertical direction atpredetermined thinning intervals to read out the pixel signals.
 5. Animage pickup apparatus comprising: an image pickup device including apixel array formed by a plurality of pixels including photoelectricconversion elements and arranged in a horizontal direction and in avertical direction, a pixel read-out unit configured to read outselected pixel signals from said pixel array, an amplifier unitconfigured to be capable of having at least two gains set therein, andamplify and output the pixel signals read out from said pixel array bysaid pixel read-out unit, and a gain-setting unit configured to setdifferent gains in said amplifier unit such that pixel signals amplifiedby the different gains can be obtained upon one-time read-out from saidpixel array by said pixel read-out unit; a photometric unit configuredto measure reflected light from an object caused by preliminary lightemission performed before shooting, based on the pixel signals read outfrom said image pickup device; a light emission amount-calculating unitconfigured to calculate a light emission amount required for theshooting, based on a result of the photometric measurement by saidphotometric unit; a light-emitting unit configured to emit light in anamount corresponding to a result of the calculation by said lightemission amount-calculating unit; and a preliminary light emissionphotometric unit configured to control said amplifier unit foraccumulation of pixel signals in said image pickup device during thepreliminary light emission, and perform photometry using at least one ofa plurality of kinds of pixel signals amplified by different gains andobtained from said image pickup device.
 6. An image pickup apparatus asclaimed in claim 5, further comprising a normal light photometric unitconfigured to control said amplifier unit for accumulation of pixelsignals in said image pickup device under a normal light condition, andperform normal light photometry using at least one of a plurality ofkinds of pixel signals amplified by different gains and obtained fromsaid image pickup device, and wherein gain configuration of saidamplifier unit for the accumulation of pixel signals in said imagepickup device under the normal light condition is identical to gainconfiguration of said amplifier unit for the accumulation of pixelsignals in said image pickup device during the preliminary lightemission.
 7. An image pickup apparatus as claimed in claim 5, having alive view function for sequentially display images based on the pixelsignals read out from said image pickup device.
 8. A method ofcontrolling an image pickup apparatus having an image pickup deviceincluding a pixel array formed by a plurality of pixels includingphotoelectric conversion elements and arranged in a horizontal directionand in a vertical direction, a pixel read-out unit configured to readout selected pixel signals from the pixel array, an amplifier unitconfigured to be capable of having at least two gains set therein, andamplify and output the pixel signals read out from the pixel array bythe pixel read-out unit, and a gain-setting unit configured to setdifferent gains in the amplifier unit such that pixel signals amplifiedby the different gains can be obtained upon one-time read-out from thepixel array by the pixel read-out unit, the method comprising: aphotometric measurement step of measuring reflected light from an objectcaused by preliminary light emission performed before shooting, based onthe pixel signals read out from the image pickup device; a lightemission amount-calculating step of calculating a light emission amountrequired for the shooting, based on a result of the photometricmeasurement in said photometric measurement step; a light-emitting stepof emitting light in an amount corresponding to a result of thecalculation in said light emission amount-calculating step; and apreliminary light emission photometric measurement step of controllingthe amplifier unit for accumulation of pixel signals in the image pickupdevice during the preliminary light emission, and perform photometryusing at least one of a plurality of kinds of pixel signals amplified bydifferent gains and obtained from the image pickup device.
 9. A programfor causing a computer to execute a method of controlling an imagepickup apparatus having an image pickup device including a pixel arrayformed by a plurality of pixels including photoelectric conversionelements and arranged in a horizontal direction and in a verticaldirection, a pixel read-out unit configured to read out selected pixelsignals from the pixel array, an amplifier unit configured to be capableof having at least two gains set therein, and amplify and output thepixel signals read out from the pixel array by the pixel read-out unit,and a gain-setting unit configured to set different gains in theamplifier unit such that pixel signals amplified by the different gainscan be obtained upon one-time read-out from the pixel array by the pixelread-out unit, the program comprising: a photometric module formeasuring reflected light from an object caused by preliminary lightemission performed before shooting, based on the pixel signals read outfrom the image pickup device; a light emission amount-calculating modulefor calculating a light emission amount required for the shooting, basedon a result of the photometric measurement by said photometricmeasurement module; a light-emitting module for emitting light in anamount corresponding to a result of the calculation by said lightemission amount-calculating module; and a preliminary light emissionphotometric module for controlling the amplifier unit for accumulationof pixel signals in the image pickup device during the preliminary lightemission, and perform photometry using at least one of a plurality ofkinds of pixel signals amplified by different gains and obtained fromthe image pickup device.